1. Field of the Invention
The present invention relates to a naphthalene compound, more specifically to a novel naphthalene compound and a naphthalene compound to be useful as an intermediate product for producing said compound and to a liquid crystal composition containing said novel naphthalene compound and a liquid crystal element using the liquid crystal composition.
2. Description of the Related Art
Liquid crystal display elements have so far widely been used for various display elements by making the best use of excellent characteristics thereof such as low voltage actuation, low power consumption, possibility of thin type display, and no fatigue of eyes because of light-receptive display element.
Among them, there have widely been used TN (twisted nematic) type liquid crystal display elements using nematic liquid crystal and STN (super twisted nematic) type liquid crystal display elements having a torsion angle adjusted from 180.degree. to 270.degree.. These display elements are nematic liquid crystal display elements using nematic liquid crystal. These nematic liquid crystal display elements have the defect that they have a long response time and therefore can provide only a response time falling on the order of some ten msec.
A recent progress in industrial techniques has been followed by strong requirement of high speed response to liquid crystal elements, and in order to meet such requirement, various attempts have been made by improving liquid crystal materials. For example, a display device making use of a photoswitching phenomenon of ferroelectric liquid crystal has been proposed Appl. Phys. Lett., 36, 899 (1980)!. The liquid crystal elements are expected to be applied to not only displays for liquid crystal televisions, etc., but also to materials for optoelectronics-related elements such as optical printer heads, optical Fourier transform elements and light valves.
Ferroelectric liquid crystals belong to tilt series chiral smectic phases in terms of a liquid crystal phase, and among them, liquid crystal phase called a chiral smectic C phase having a low viscosity is preferred from a viewpoint of practical use. Various liquid crystal compounds showing chiral smectic C phases have so far been investigated, and a lot of compounds have already been found and produced. Conditions for using them for ferroelectric liquid crystal elements include:
showing a chiral smectic C phase in a wide temperature range including room temperature, PA1 having a suitable phase series on a high temperature part of a chiral smectic C phase and large helical pitches thereof in order to obtain good orientation, PA1 having a suitable tilt angle, PA1 having a low viscosity, PA1 having spontaneous polarization which is large to some extent, and the like.
No single ferroelectric liquid crystal which can satisfy these conditions has ever been known. Accordingly, ferroelectric liquid crystal compositions obtained by blending several liquid crystal compounds or non-liquid crystal compounds have to be used in practical uses.
A ferroelectric liquid crystal composition does not always comprise only ferroelectric liquid crystal compounds, and it is disclosed in, for example, Japanese Patent Application Laid-Open No. 61 195187 (1986) that compositions showing ferroelectric liquid crystal phases as a whole can be obtained by employing compounds or compositions showing non-chiral smectic C, F, G, H and I phases for fundamental materials and blending them with one or plural compounds showing ferroelectric liquid crystal phases. Further, it is reported that ferroelectric liquid crystal compositions can be obtained as a whole by employing compounds or compositions showing phases such as a non-chiral smectic C phase for fundamental materials and blending them with one or plural compounds which are optically active but do not show ferroelectric liquid crystal phases Mol. Cryst. Liq. Cryst., 89, 327 (1982)!.
Phenylpyrimidine series liquid crystal compounds and phenylbenzoate series liquid crystal compounds as shown below have so far been known as typical compounds showing chiral smectic C phases: ##STR3## wherein R represents an alkyl group, and R* represents an optically active alkyl group.
Further, naphthalene series liquid crystal compounds as shown below are proposed in Japanese Patent Application Laid-open No. 63-246346 (1988), Japanese Patent Application Laid-open No. 1-193390 (1989), Japanese Patent Application Laid-open No. 3-68686 (1991) and Japanese Patent Application Laid-open No. 3-106850 (1991): ##STR4## wherein R represents an alkyl group, and R* represents an optically active alkyl group.
However, ferroelectric liquid crystal compositions using the phenylpyrimidine series liquid crystal compounds or phenylbenzoate series liquid crystal compounds described above have had the problems that they are liable to cause orientation unevenness so as to bring about defects when they are put into liquid crystal cells and that the good memory property can not be obtained and the contrast ratio is low. Meanwhile, ferroelectric liquid crystal compositions comprising the naphthalene series compounds described above show good orientation when liquid crystal cells are charged with them, and can provide a good memory property without having defects. However, it is not reasonable to say that they have sufficiently satisfactory characteristics in terms of high speed response and temperature dependency of a response time.